Harnad, S. (1995) Why and How We Are Not Zombies. Journal of Consciousness Studies1: 164-167. (Presented at Royal Society/Association of British Sciences Writers
Press Conference on "Consciousness: Its Place in Contemporary Science" Tuesday
7 February 10am - 12:50 am at the Royal Society)

ABSTRACT: A robot that is functionally indistinguishable from us may or may not be
a mindless Zombie. There will never be any way to know, yet its functional
principles will be as close as we can ever get to explaining the mind.

Let us not mince words. The difference between something that is and is
not conscious is that something's home in something that's conscious, something
experiencing experiences, feeling feelings, perhaps even, though not necessarily,
thinking thoughts. Don't be lured into details about "self-awareness" and
"intentionality." If there's something home in there, something hurting
when pinched, then that's a mind and we are faced squarely with two age-old
philosophical problems:

The first is: How can we know whether or not something's home in there?
We aren't mind-readers. Not even a brain surgeon can guarantee that a patient
is conscious. This is called the "other-minds" problem, and it's important
to note that it is unlike any other problem in science having to do with
the existence or reality of something that is unobservable. Quarks, like
consciousness, cannot be observed directly, but there are many things that follow from quarks' existing or not existing, and those things can be observed. Does anything follow from the existence of consciousness,
that would not follow just as readily if we were all Zombies who merely acted exactly as if they were conscious?

Think about it: Zombies who acted exactly as if they were conscious: Acted
for how long? Well, for a lifetime obviously. And what does "exactly" mean?
It means that there is no way to tell them apart from one of us based on
anything they do. Zombies are functionally equivalent to and functionally indistinguishable
from ourselves.

"So cut them apart," you say, "and check what's inside. If it's different
from what's in us, that's still an observable difference, and we could conclude
from that that they were just unconscious Zombies."

But could we really draw that conclusion if they were made of different
stuff? What if they came from another planet: Would the fact that their
innards were different be enough to convince you that they didn't feel pain
when they were pinched and screamed? Would you yourself like to submit to
such a verdict on another planet?

Or would you feel more comfortable pronouncing such a verdict if they didn't
come from another planet, but were built in a lab here on earth? Is there
something about that that guarantees that their screams are not genuine?
If you feel there is, then you must feel that you know something about the
solution to the second philosophical problem, the mind/body problem:

What is consciousness? Let us assume that, whatever it is, it isn't an extra
"force" in nature, on a par with electricity or gravity, for otherwise all
our thoughts would be telekinetic, mind moving matter, and high energy psychic
forces would be duelling with their "duals," high energy physics forces,
not only in the world as a whole, but in the Academy in particular, with
the prize being the truth or falsity of the laws of energy conservation
and perhaps even causality itself.

So we will assume, instead, that consciousness is not an autonomous force,
but some property or aspect of the ordinary physical forces we already know.
If so, then it is incumbent on anyone who thinks he can tell the Zombie
from the real thing that he be able to say what this property is. This is
a notoriously difficult thing to do; in fact, I'm willing to bet it's impossible,
and will even say why:

Pick a property. Any property. It can be anatomical, physiological, chemical
or even "functional." Suppose that that property is what determines whether
or not something is conscious. Now answer the following two questions:

(1) How could you ever determine whether that supposition -- that that's
the property that distinguishes conscious things from unconscious ones --
was correct? That's the other-minds problem again.

But now let's suppose that the supposition -- that that's the property that
distinguishes conscious things from unconscious ones -- was, miraculously,
true, even though there was no way we could know it was true:

(2) In what, specifically, would its truth consist? What is it that something
would lack if it lacked consciousness yet had the property you picked out?
For if you pick anything other than consciousness itself as the thing it
would lack if it lacked that property that was supposed to be the determinant
of consciousness (which would be a bit circular), then one can always say:
why can't it have that property without the consciousness? And no one has
even the faintest inkling of what could count as a satisfactory answer to
that question.

Console yourself with the fact that you are not alone, in facing this problem.
It's not just centuries of philosophers who have wrestled with it in vain
(and don't let anyone tell you the problem's only as old as Descartes, or
that it's Descartes' fault, or anything like that: the problem of mind is
as old as philosophy and it besets anyone who reflects on the nature of
the mind): In particular, it is not only neurosurgeons, experimental psychologists,
and ordinary people who are not mind-readers: The Blind Watchmaker (Who
designed us though trial and error based on random mutations and their consequences
for survival and reproduction) is no mind-reader either. He could not have
let the conscious ones through and exclude the Zombies, because the two
are functionally equivalent and functionally indistinguishable, and survival
and reproduction are purely functional matters!

So what's a scientist to do, if he makes the mistake of staking out the
mind as his terrain of inquiry? If the other-minds and mind/body problem
are insoluble, does that mean that the mind is not scientifically investigable?

Only that it cannot be investigated directly, the way most things are investigated.
It can be investigated indirectly, however, and perhaps eventually cornered
by a series of approximations. Consider that we have been pretty cavalier
about the problem of designing a Zombie: Doing it is not as easy as imagining
it. There are plenty of formidable scientific problems to solve before we
need to begin worrying about whether or not the functionally equivalent
Zombies we've designed are conscious: We first have to generate their functional
capacities.

Actually, I think scientific mind-theory is better described as reverse
bioengineering: Ordinary engineering applies basic physics and engineering
principles to the design of systems with certain functional capacities that
are useful to us [bridges, ovens, planes, computers], whereas a scientific
theory of mind would first have to successful second-guess what gives creatures
like us, already ready-made by the Blind Watchmaker, our functional capacities.

So the road ahead of us is pretty clear for the time being, even though
we have reason to believe there is a cloud at the end of it. For now, we
need to devote our time and ingenuity to second-guessing those functional
capacities until we manage to scale up to a Zombie. It should be some consolation
that the usual rules of scientific inquiry are in effect for the functional
part of our quest. It's easy to reverse-engineer a few isolated pieces of
our functional capacity, and there are many different ways to do it, but
as the functional chunk we take on gets bigger and bigger, the number of
different ways it can be successfully generated gets smaller and smaller.

This is ordinary scientific underdetermination: You can always predict and
explain a small body of data in lots of ways, most or all of which have
nothing to do with reality. But as you predict and explain more and more
data, your degrees of freedom shrink and your theory gets more powerful
and general. The hope, in all areas of science, is that when it is complete,
and predicts and explains all observable data, then your theory will have
converged on reality; it will be the true theory of the way things are.
It might not be. Perhaps there will be another theory that explains it all
too, and there won't be any way to know which one's true. (Even picking
the simpler theory, if one of them is simpler than the other, may not be
the right choice, because the world may simply not happen to be the simplest
one it might have been, while still preserving all appearances.)

This is very much the way I think it will be at the end of the day (or at
the end of the road, rather, if we stick to our previous metaphor), when
we have reverse-engineered a complete Zombie, functionally equivalent to
and functionally indistinguishable from us in any way. There is of course
the possibility that there will be several, radically different, but equally
successful Zombie designs. Cutting them (and ourselves) up, at that point,
may be the only remaining way to narrow down the differences. We could insist
that in the case of the reverse engineering of the mind, "all the observable
data" means not only all the behavioral data, but all the neural data too,
and we may want to put our money only on the Zombie that is indistinguishable
from us in both respects.

I somehow doubt that will be necessary though. I really think that the task
of generating our full Zombie capacity probably already narrows the degrees
of freedom enough to exclude all nonconscious candidates. I draw some solace,
for example, from the fact to which I have already drawn attention, namely,
that the "forward engineer" (the Blind Watchmaker) whose work we are reverse
engineering had nothing stronger to go by either. But does this mean that
the mind/body problem is really just another example of scientific underdermination
that will be settled by whatever candidate makes it to the home stretch
at the end of the day?

Not quite. For that would be all there was to it if consciousness were like
quarks, that other example of an unobservable that I mentioned earlier.
One can, without too much loss of sleep, accept that if the winning theory
says there are quarks -- because with quarks it can predict and explain
all the observable data, whereas without them it can't -- then it's safe
to accept that there are indeed quarks.

But I have to remind you that our complete reverse engineering theory, the
one that generates our full Zombie capacity, will be entirely mute about
consciousness, and will be just as capable of predicting and explaining
all the observable data with or without the supposition that the Zombie
is conscious.

Perhaps another way of putting it is that the complete Zombie theory will
explain all the data except one: The fact of the existence of consciousness
itself. This fact is at the heart (or rather the mind) of the very idea
of "observation," and it's a fact that each of us can "observe" to be true
in his own particular case.

So clearly the Zombie theory has left something out. Hence there is still
something different here, something special about the mind/body problem,
and something that eludes a scientific theory of mind unlike anything analogous
in a scientific theory of matter. Maybe it's safe to assume that consciousness
will somehow piggyback on Zombie capacity; maybe not. It might be some consolation
that if it doesn't, we can never hope to be the wiser. But I think it's
nothing to lose sleep about, at least not for a long time to come.

Harnad, S. (1993) Turing Indistinguishability and the Blind Watchmaker.
Presented at Conference on "Evolution and the Human Sciences" London School
of Economics Centre for the Philosophy of the Natural and Social Sciences
24 - 26 June 1993.